The present invention is directed to a built-up support member for carrying bending loads and is formed of two coacting load carrying separate elements one superimposed on the other. The separate elements absorb normal forces caused by bending. The separate elements have contacting surfaces and include means for transmitting shear forces acting at the contacting surfaces.
In various types of construction, reinforced concrete elements are often used as load bearing elements, for instance as ceilings, in bridges and in other load bearing structures. In some instances large quantities of concrete are utilized, however, the concrete does not afford any load carrying function, instead it provides protection against corrosion for steel members located inside the concrete. By comparison, lighter members can often be employed and other advantages obtained by the use of built-up load carrying members of equal stiffness. A built-up load bearing support member is formed of at least two separate elements. The separate elements constituting such a built-up support member can be a concrete panel and a timber girder or beam cooperating with the panel. This type of support member is used when bending forces are experienced, whereby the concrete panel carries the compression load and the wooden beam the tensile load. This division of the load involves the development of shear forces between the separate elements of the built-up support member.
Such shear forces must be transmitted by suitable attachment or connecting means. Dowels can be used as shear transmission means, connected into the concrete element and also into the wooden element or beam with the connection to the beam effected by a thread. A large quantity of dowels is necessary for a positively locked transmission of the shear forces acting on the joint between the two elements. If the dowels provide incomplete frictional transmission of the shearing forces, the dowels are stressed in transverse directions and become loosened with the support member experiencing a loss in stiffness.
In another known built-up support member, a diagonal dowel connection has been used where the dowels are arranged sloping relative to the major dimensions of the member. In such an arrangement a large quantity of dowels are necessary, however, the diagonally arranged dowel connection is also prone to loosening. To obtain an improved transmission of the shear forces, positively locked connection between the load bearing separate elements have been known, such as described in the French patent application 2568610.
This known connection has the disadvantage, however, that the vibration which develops in the concrete and wooden elements can result in a loosening of the positively locked connection and results in a considerable loss in stiffness of the built-up support member.